image_view: Bind properties in UI file

data/gtk/image_view.ui

@@ -18,6 +18,7 @@
               <object class="GtkHeaderBar" id="headerbar">
                 <property name="valign">start</property>
                 <property name="show-title-buttons">False</property>
+                <property name="visible" bind-source="IvImageView" bind-property="header-visible" bind-flags="sync-create"/>
                 <child type="end">
                   <object class="GtkButton">
                     <property name="margin-start">6</property>

src/widgets/image_view.rs

@@ -130,12 +130,6 @@ mod imp {
         fn constructed(&self, obj: &Self::Type) {
             self.parent_constructed(obj);
 
-            obj.bind_property("header-visible", &*self.headerbar, "visible")
-                .flags(glib::BindingFlags::BIDIRECTIONAL)
-                .flags(glib::BindingFlags::SYNC_CREATE)
-                .build()
-                .unwrap();
-
             self.click_gesture
                 .connect_pressed(clone!(@weak obj => move |_, _, x, y| {
                     obj.show_popover_at(x, y);